So i had this idea for monoshock on a puch. I don't know how good it might be, but it looks nice drawn out.
It would make use of the current swingarm, or a new one. You'd have to add some more tubing or something to mount the shock with, and then some frame modification as well. Run the shock into the frame, it's not outside of the frame. You'd maybe have to brace the frame inside, but if the shocks work stock mounted on that fender, it should be no problem. You'd also have to cut the frame to make room for the modified swingarm to swing.
Otherwise you could chose to mount that shock elsewhere in the frame.. but i was thinking of covering the mounting point with the sidecover.
I'll probably draw it up 3d later, so it's easier to understand. Let me know if you think it's any good.
Here's a swingarm to get the idea of how it would be i guess. I thought maybe like a bend tube near the back going from one side of the tire to the other, instead of that single one, but pretty similar to this.